Polymer gels are semi-solid systems that respond in a liquid like fashion under certain circumstances but their molecules do not have motion that is independent of each other, hence they behave like solids in other circumstances.
Gels can be synthesised as physical gels where a cross-linked network is swelled by a non reactive liquid. Without the presence of this swelling medium the cross-linked network would be a solid. Silicone gels currently used in breast implants are physical gels where a cross-linked polydimethylsiloxane (PDMS) system is swollen by a non reactive, low molecular weight PDMS. These gels are inherently prone to leakage of the low molecular weight liquid PDMS and contain heavy metal catalysts such as platinum and tin which can leach out of the implant in an in-vivo situation.
Hydrogels are other examples of physical gels, where hydrophilic groups in the cross-linked network can attract water molecules and are swollen by them. In a physical gel the parts by weight of the swelling medium can be as high as 90%. This swelling medium can be extracted out of the gel by most solvents and biological fluids.
There is a need for a gel that mimics the behaviour of a PDMS-based physical gel, but is chemically formulated so as to avoid the complications of a physical gel.